Method for establishing a link between two communication facilities

ABSTRACT

The invention relates to a method for establishing a link through which at least one data stream is to be transmitted. A first communication facility and a second communication facility form a first and second end of the link, respectively. A first base station is connected to the first communication facility, and a second base station is connected to the second communication facility, the first base station having preselected the second base station from among a plurality of base stations. The method includes the following steps, implemented by the first communication facility: extracting an identifier of the first base station and an identifier of the second base station, said identifiers being included in a message transmitted by the first base station; and establishing the link between the first communication facility and the second communication facility from the extracted identifier of the first base station and the extracted identifier of the second base station.

The invention relates to the field of telecommunications, and moreparticularly, to mobile access networks.

The document of the 3GPP (3rd Generation Partnership Project), referenceTS 36.300 v.9.3.0 proposes developments relating to architectures forthe mobile access network.

More precisely, the document TS 36.300 v.9.3.0 describes a mechanismknown as ANR (Automatic Neighbor Relationship). Such an ANR mechanism isimplemented by base stations with the aim of discovering neighboringbase stations. The base stations capable of implementing the ANRmechanism comprise means of selecting, from amongst a plurality ofneighboring base stations, one or more base stations offering a radiocoverage guaranteeing a satisfactory level of quality of service andthat are able to be candidates with a view to the attachment of a mobileterminal during a cell handover procedure or for exchanging data betweenneighboring base stations in order to optimize the management of theradio resources of a mobile access network. Thus, when a first basestation selects a second base station, referred to as neighboring basestation, by implementing the ANR mechanism, the first base stationinforms a Mobility Management Entity or MME of this fact which entity inturn informs the second base station of this. Such a solution offersflexibility in the selection, by the first base station, of a candidatebase station with a view to the attachment of a mobile terminal during ahandover procedure or during exchanges of data between base stations.

Such a solution allows a dynamic selection of the second base station.Indeed, the selection of the second base station is based onmeasurements of radio reception power reported by various mobileterminals connected to the first base station rather than on the basisof parameter determinations carried out during the start-up phase of themobile communications network.

The neighboring base stations being predefined by parameter setup in thefirst base station, the data transfer scheme is also predefined as afunction of the setup.

Thus, when the first base station implements the ANR mechanism, thetransfer scheme is not adapted. Indeed, a base station considered as aneighbor of the first base station during the parameter setup of thelatter might not be a neighboring base station when the first basestation implements the ANR mechanism and vice versa. Consequently, thetransfer scheme for the data is not adapted to the needs of the basestations when the latter implement the ANR mechanism.

One of the aims of the invention is to overcome the drawbacks of theprior art.

For this purpose, the invention provides a method for establishing alink in the OSI layer 2 or 3 via which at least one data stream isintended to be transmitted, a first unit of communications equipment anda second unit of communications equipment respectively forming a firstand a second end of the link, a first base station being connected tothe first unit of communications equipment, and a second base stationbeing connected to the second unit of communications equipment,characterized in that, the first base station having selected the secondbase station from amongst a plurality of base stations in anticipationof a handover procedure, the method comprises the following stepsimplemented by the first unit of communications equipment:

-   -   extraction of an identifier of the first base station and of an        identifier of the second base station comprised in a message        sent by the first base station,    -   establishment of the link between the first unit of        communications equipment and the second unit of communications        equipment based on the identifier of the first base station and        on the identifier of the second base station extracted.

Such a solution allows the transfer scheme for the data to be adapted tothe needs of the base stations when the latter have identified the basestation or stations that may be candidates with a view to the attachmentof a mobile terminal during a handover procedure or exchanges of databetween neighboring base stations. In the framework of the invention, alink is understood to mean a logical link supported by a physicalconnection such as a section of optical fiber or a copper pair. In theframework of the invention, a link is an OSI (Open SystemsInterconnection) model connectivity of level 2 or of level 3 such asdefined by the ISO (International Standards Organization). It will benoted that, in the framework of the invention, a base station isconnected to a unit of communications equipment by this type of link.

The establishment of a link intended to transmit data between a firstand a second base station is triggered once the second base station hasbeen selected as a neighboring base station by the first base station incontrast to the architectures of the prior art.

It may also be noted that, in a second step, the method is alsoimplemented symmetrically by the second unit of equipment in order toestablish the link in the other direction, in other words between thesecond and the first unit of equipment.

Indeed, the second base station having initially selected the first basestation from amongst a plurality of base stations, the method comprisesthe following steps implemented by the second unit of communicationsequipment:

-   -   extraction of an identifier of the second base station and of an        identifier of the first base station comprised in a message sent        by the second base station,    -   establishment of the link between the second unit of        communications equipment and the first unit of communications        equipment based on the identifier of the second base station and        on the identifier of the first base station extracted.

When the method is implemented by the first unit of equipment, theselection of the second base station is carried out by the first basestation on the basis of information uploaded by the mobile terminal inthe framework of the ANR mechanism previously described.

When the method is implemented by the second equipment, the selection ofthe first base station is carried out by the second base station on thebasis of information downloaded from a unit of equipment of the networkresponsible for the management of the mobility of the mobile terminalssuch as a mobility management equipment MME.

The subject of the invention is a solution that thus allows resources ofthe network to be saved because only links intended to transmit a datastream between two units of communications equipment are establishedavoiding an unnecessary reservation of the resources of the network incontrast to the architecture model known as ‘full-mesh architecture’. Insuch an architecture model, links are established between all thecommunications equipment in such a manner that data streams can beexchanged between all the base stations then consuming resources of thenetwork without this being necessary.

The solution which is the subject of the invention also offers aflexibility in the establishment of the links since the latter is doneas needed; such a solution is thus advantageous during the use of thenetwork in contrast to the architecture model known as ‘partial-mesharchitecture’. In such an architecture model, links are establishedbetween certain units of communications equipment when the network isput into service. Such links are established statically such that theresources associated with these links are used even if the link becomesobsolete during the use of the network or, conversely, links are notestablished even though they prove to be useful. This solution implies atight relationship between various units of equipment of the networkwhich must update their respective manager with regard to the topologyof the mobile access network.

In one embodiment of the invention, the first unit of communicationsequipment intercepts a message sent by the first base station to a unitof equipment of the network responsible for the management of themobility of the mobile terminals such as a mobility management equipmentMME.

In another embodiment, in addition to the message sent to a mobilitymanagement equipment MME, the first base station also sends a specificmessage to the first unit of communications equipment.

According to one feature of the method for establishing a link which isa subject of the invention, the phase for establishing the linkcomprises:

-   -   a step for broadcasting, to a plurality of communications        equipment, the identifier of the first base station, as an        identifier of a route allowing a connection to the first base        station,    -   a step for comparison of an identifier of another base station,        broadcast to a plurality of communications equipment including        the first unit of communications equipment, by another unit of        communications equipment as an identifier of a route allowing a        connection to the other base station, with the identifier of the        second base station extracted,    -   in the case where the identifier of the base station broadcast        is identical to the identifier of the second base station        extracted, a step for storing the identifier of the route        allowing a connection to the second base station.

The first unit of communications equipment broadcasts the identifier ofthe first base station to other communications equipment with a view toestablishing a link with a unit of communications equipment connected toa base station that may be a candidate with a view to the attachment ofa mobile terminal during a handover procedure or exchanges of databetween neighboring base stations.

Thus, when the first unit of communications equipment receives a messagebroadcast by another unit of communications equipment comprising theidentifier of another base station, it compares this identifier with theidentifier of the second base station. If the identifier of the otherbase station comprised in the message broadcast corresponds to theidentifier of the second base station associated with the identifier ofthe first base station by the first unit of communications equipment,then the establishment of the link between the first and the second unitof communications equipment is completed and the link is established.

According to one feature of the method for establishing a link which isa subject of the invention, the phase for establishing the linkcomprises:

-   -   a step for creating a first point of attachment in the first        unit of communications equipment intended to form the first end        of the link,    -   a step for determining an identifier of a second point of        attachment in the second unit of communications equipment        intended to form the second end of the link,    -   a step for sending a request for establishing the link to the        second unit of communications equipment, the request for        establishing the link comprising the identifier of the first        point of attachment and the identifier of the second point of        attachment.

In this embodiment, the link intended to be established between thefirst and the second unit of communications equipment, which is apseudo-link such as defined in a document of the IETF (InternetEngineering Task Force, a grouping for standardization of the Internet),referenced RFC 3985 (RFC stands for “Request For Comments”) under theterm “pseudo-wire”, allows the transmission of packets of data notconforming to the IP protocol, such as for example packets of dataconforming to the Ethernet protocol.

The invention further relates to a method for communicating between abase station and a unit of communications equipment to which the basestation is connected, the base station selecting from amongst aplurality of base stations, in anticipation of a handover procedure, asecond base station connected to a second unit of communicationsequipment, a link in the OSI layer 2 or 3 via which at least one datastream is intended to be transmitted, the link being intended to beestablished between the first and the second unit of communicationsequipment, characterized in that the method comprises a step for sendinga message, to the first unit of communications equipment, comprising anidentifier of the first base station and an identifier of the secondbase station.

The base station communicates with the first unit of equipment by meansof protocols such as the BGP (Border Gateway Protocol) which is aprotocol for exchange of routes. Conventionally, the base stationinforms the first unit of communications equipment of its IP prefixes.In the framework of the invention, the BGP messages exchanged betweenthe first base station and the first unit of communications equipmentcomprise at least one additional field in which an identifier of thefirst base station and an identifier of the second base station arespecified.

It may be noted that this method of communication is also implementedsymmetrically by the second base station in order to establish the linkin the other direction, in other words between the second and the firstunit of equipment.

The invention also relates to a unit of communications equipment forminga first end of a link in the OSI layer 2 or 3 via which at least onedata stream is intended to be transmitted, a second unit ofcommunications equipment forming a second end of the link, a first basestation being connected to the unit of communications equipment, and asecond base station being connected to the second unit of communicationsequipment, characterized in that, the first base station having selectedthe second base station from amongst a plurality of base stations inanticipation of a handover procedure, the unit of communicationsequipment comprises:

-   -   means of extraction of an identifier of the first base station        and of an identifier of the second base station comprised in a        message sent by the first base station,    -   means for establishing the link between the first unit of        communications equipment and the second unit of communications        equipment based on the identifier of the first base station and        on the identifier of the second base station extracted.

Finally, another subject of the invention is a base station, connectedto a first unit of communications equipment, selecting from amongst aplurality of base stations, in anticipation of a handover procedure, asecond base station connected to a second unit of communicationsequipment, a link in the OSI layer 2 or 3 via which at least one datastream is intended to be transmitted, the link being intended to beestablished between the first and the second unit of communicationsequipment, characterized in that it comprises means for sending, to thefirst unit of communications equipment, a message comprising anidentifier of the base station and an identifier of the second basestation.

In one variant, the message also comprises a parameter indicating thatthe identifier of the base station is intended to be used for theestablishment of the link.

According to other aspects, the invention also relates to computerprograms comprising program code instructions for the implementation ofthe steps of the link establishment and communication methods previouslydescribed, when these programs are executed by a computer.

Each of the computer programs described hereinabove can use any givenprogramming language, and may be in the form of source code, objectcode, or of a code intermediate between source code and object code,such as in a partially compiled form, or in any other desired form.

The invention is also aimed at a recording medium readable by a computeron which a computer program such as previously described is recorded.

The information medium may be any given entity or device capable ofstoring the program. For example, the medium can comprise a storagemeans, such as a ROM (for “Read Only Memory”), for example a CD ROM or amicroelectronic circuit ROM, or again a means of magnetic recording, forexample a diskette (floppy disk) or a hard disk.

On the other hand, the information medium can be a transmissible mediumsuch as an electrical or optical signal, which may be transported via anelectrical or optical cable, by radio or by other means. The programaccording to the invention may in particular be downloaded/uploaded overa network of the Internet type.

Alternatively, the information medium may be an integrated circuit intowhich the program is incorporated, the circuit being designed to executeor to be used in the execution of the method in question.

Other features and advantages will become apparent upon readingembodiments described with reference to the drawings in which:

FIG. 1 shows a mobile access network in which the method forestablishing a link and the method of communication are implemented,

FIG. 2 shows the steps of the method of communication,

FIGS. 3A and 3B show messages sent by the base station to thecommunications equipment,

FIG. 4 shows the steps of the method for establishing a link,

FIG. 5 shows a diagram of the exchanges between the various units ofequipment of the mobile access network in a first embodiment,

FIG. 6 shows a diagram of the exchanges between the various units ofequipment of the mobile access network in a second embodiment,

FIG. 7 shows a diagram of the exchanges between the various units ofequipment of the mobile access network in a third embodiment,

FIG. 8 shows a base station implementing the method of communicationwhich is a subject of the invention,

FIGS. 9A, 9B, and 9C show a unit of communications equipmentimplementing the method for establishing a link which is a subject ofthe invention.

FIG. 1 shows a mobile access network R in which the link establishmentand communication methods which are the subjects of the invention areimplemented.

Such a mobile access network R comprises a plurality of units ofcommunications equipment PE_(i), i ∈{1, 4} connected to one another bymeans of wired links such as copper pairs. Such units of communicationsequipment PE_(i) are for example routers.

Thus, a first unit of communications equipment PE₁ is connected via afirst link L2 to a second unit of communications equipment PE₂. The unitof communications equipment PE₂ is connected to a third unit ofequipment PE₃ by means of a link L3. The unit of communicationsequipment PE₃ is connected, by means of a link L4, to a fourth unit ofcommunications equipment PE₄. The equipment PE₄ is connected to theequipment PE₁ by means of a link L5.

A first base station SB₁ is connected to the unit of communicationsequipment PE₁ by means of a link L1 such as a section of a copper pair.

A second base station SB₂ is connected to the unit of communicationsequipment PE₂ by means of a link L7 such as a section of a copper pair.

A third base station SB₃ is connected to the unit of communicationsequipment PE₂ by means of a link L8 such as a section of a copper pair.

A fourth base station SB₄ is connected to the unit of communicationsequipment PE₃ by means of a link L9 such as a section of a copper pair.

A unit of equipment for mobility management MME is connected to the unitof communications equipment PE₄ by means of a link L6.

The base stations SB₁, SB₂, SB₃ and SB₄ implement the ANR mechanism forselecting, from amongst a plurality of neighboring base stations, one ormore base stations, referred to as neighboring base stations, offering aradio coverage guaranteeing a satisfactory level of quality of serviceand which can be candidates with a view to the attachment of a mobileterminal during a cell handover procedure or for exchanging data betweenneighboring base stations in order to optimize the management of theradio resources of a mobile access network.

With reference to FIG. 2, in order to select a neighboring base station,the base station SB₁ implements the ANR mechanism. During a step E1, thebase station SB₁ implements a step for selection of a neighboring basestation from amongst the base stations SB₂, SB₃, SB₄. At the end of thestep E1, the base station SB₂ is selected. The base station SB₁ is awareof an identifier IdSB₂ of the base station SB₂. Only the base stationsnot having already been selected by the first base station SB₁ and thebase stations whose selection via the ANR mechanism is not prohibited bythe operator manager of the network R can be selected by the basestation SB₁.

Once the neighboring base station has been selected, during a step E2,the base station SB₁ sends a message MSG comprising an identifier of thefirst base station IdSB₁ and the identifier of the second base stationIdSB₂.

In a first variant embodiment, the message MSG sent by the base stationSB₁ is sent to the mobility management equipment MME.

In a second variant embodiment, the base station SB₁ sends, in additionto the message MSG, a second message MSG1 to the unit of communicationsequipment PE₁. Such a message MSG1 is for example a message conformingto the BGP (Border Gateway Protocol) protocol. However, such a messageMSG1 comprises additional fields with respect to a message conforming tothe conventional BGP protocol.

In a first variant embodiment shown in FIG. 3A, the message MSG1comprises, in a first field known as NLRI field, IP prefixes of the basestation SB₁, in a second field known as Next Hop an IP address @IP SB₁chosen from amongst the IP prefixes pref IP SB₁ of the base station SB₁,and finally, in two new fields, the identifier of the first base stationIdSB₁ and the identifier of the second base station IdSB₂.

In a second variant embodiment shown in FIG. 3B, the message MSG1comprises, in a new NLRI field, the identifier IdSB₁ of the base stationSB₁, in a second field known as Next Hop, an IP address @IP SB₁ of thebase station SB₁, and finally, in a new field, the identifier of thesecond base station IdSB₂.

In one variant embodiment of the invention, the message MSG1 can be amessage conforming to the OSPF (Open Shortest Path First), ISIS(Intermediate system to intermediate system) or else ANCP (Access NodeControl Protocol) protocols. However, such a message MSG1 comprises anadditional field with respect to messages conforming to these variousconventional protocols.

The unit of communications equipment PE₁ then implements the method forestablishing the link T between the unit of communications equipment PE₁and the unit of communications equipment PE₂.

With reference to FIG. 4, the unit of communications equipment PE₁extracts from the message MSG, MSG1, sent by the base station SB1, theidentifier of the first base station IdSB₁ and the identifier of thesecond base station IdSB₂ comprised in the message sent by the firstbase station SB₁ during a step F1.

Once this information has been extracted from the message MSG, MSG1,sent by the base station SB₁, the unit of communications equipment PE₁triggers the establishment of the link T during a step F20.

Such a method for establishing a link between a first unit ofcommunications equipment PE₁ and a second unit of communicationsequipment PE₂ allows the transfer scheme for the data to be adapted tothe needs of the base station SB₁ when the latter has identified thebase station or stations that may be candidates with a view to theattachment of a mobile terminal during a cell handover procedure. Itwill therefore be understood that the base station SB₁ has selected atleast one other base station in anticipation of a handover procedure.

In a first variant embodiment, the unit of communications equipment PE₁intercepts the message MSG sent by the base station SB₁ to the equipmentfor management of the mobility MME during a step F0.

In a second variant embodiment, the unit of communications equipmentreceives the message MSG1 sent by the base station SB₁ during a step F0b.

In a first embodiment of the invention shown in FIG. 5, the link T to beestablished between the unit of communications equipment PE₁ and theunit of communications equipment PE₂ is an IP connectivity supplied by aL3VPN (Level 3 Virtual Private Networks) service such as defined in thedocument RFC4364. Such a solution relies on the implementation of MPLS(Multi-protocol Label Switching) technology for the transport of thedata between the two ends of the link T. MPLS technology includes theaddition, in a header of the data to be transmitted, of one or morelabels containing information allowing the communications equipment ofthe network R to determine the next stage that the data must follow inorder to reach its destination.

In this first embodiment of the invention, the unit of communicationsequipment PE₁ extracts from a message MSG, MSG1, sent by the basestation SB₁, the identifier of the first base station IdSB₁, theidentifier of the second base station IdSB₂ during the step F1.

During a step F21, the unit of communications equipment PE₁ stores theidentifier IdSB₁ of the base station SB₁ and the identifier IdSB₂ of thebase station SB₂.

During a step F22, the unit of communications equipment PE₁ broadcaststo the communications equipment PE₂, PE₃ and PE₄ the identifier of thefirst base station IdSB₁, as an identifier of a route allowing aconnection to the first base station SB₁. According to the BGP routingprotocol, such a route identifier is called a “Route Target”.

During a step F23, the unit of communications equipment PE₁ receives,from the units of communications equipment PE₂, PE₃, PE₄, the respectiveidentifiers of the base station IdSB₂, of the base station IdSB₃, and ofthe base station IdSB₄ as identifiers of routes respectively allowingconnections to the base station SB₂, the base station SB₃, and the basestation SB₄.

During a step F24, the unit of communications equipment PE₁ implements astep for comparison of the identifiers of the base stations IdSB₂,IdSB₃, and IdSB₄, received during the step F23 with the identifier ofthe second base station IdSB₂ extracted from the message MSG, MSG1.

In the case where one of the broadcast identifiers of base stationsIdSB₂, IdSB₃ or IdSB₄ is identical to the identifier of the second basestation IdSB₂ extracted from the message MSG, MSG1, the unit ofcommunications equipment PE1 stores, during a step F25, the identifierIdSB₂ of the route allowing a connection to the second base station SB₂.This step for storing the route for reaching the second base station SB₂completes the establishment of the link T between the first unit ofcommunications equipment PE₁ and the second unit of communicationsequipment PE₂.

In parallel, the base station SB₁ sends a message MSG to the mobilitymanagement equipment MME. The message MSG comprises the identifier ofthe base station SB₁ and the identifier of the base station SB₂ togetherwith information indicating that these two base stations SB₁, SB₂ areneighbors.

The mobility management equipment MME then transmits a message MSG′ tothe base station BS₂ during a step F26. This step allows the second basestation BS₂ to obtain the identifier IdSB₁ of the first base stationSB₁.

Upon receiving this message MSG′, the steps F1 to F25 previouslydescribed are implemented by the unit of communications equipment PE₂ inorder to establish the link T for the direction of communication—unit ofcommunications equipment PE₂ toward unit of communications equipmentPE₁—such that the link T is bidirectional.

Since the transport of the data via the link T is carried out accordingto the MPLS technique, each unit of communications equipment PE_(i) ofthe network R is identified by a label lbl_(i). This label lbl_(i)allows any given unit of communications equipment PE_(i) to establish aconnectivity according to the MPLS technique with another unit ofcommunications equipment.

Thus, once the link T is established between the units of communicationsequipment PE₁ and PE₂, the latter exchange their respective labels lbl₁and lbl₂. The label lbl₁ is added by the second unit of communicationsequipment PE₂ in the header of the data intended to be sent toward thefirst unit of communications equipment PE₁ via the link T. Similarly,the label lbl₂ is added by the first unit of communications equipmentPE₁ in the header of the data intended to be sent toward the second unitof communications equipment PE₂ via the link T.

In a second embodiment of the invention shown in FIG. 6, the link T tobe established between the unit of communications equipment PE₁ and theunit of communications equipment PE₂ is an Ethernet connectivitysupplied by the BGP L2VPN (Level 2 Virtual Private Networks) servicesuch as defined in the document RFC4761.

Such a solution also relies on the implementation of MPLS technology forthe transport of the data between the two ends of the link T.

In this second embodiment of the invention, the unit of communicationsequipment PE₁ extracts from a message MSG, MSG1, sent by the basestation SB₁, the identifier of the first base station IdSB₁ and theidentifier of the second base station IdSB₂ during the step F1.

During a step F21, the unit of communications equipment PE₁ stores theidentifier IdSB₁ of the base station SB₁ and the identifier IdSB₂ of thebase station SB₂.

During a step F22, the unit of communications equipment PE₁ broadcaststo the communications equipment PE₂, PE₃ and PE₄, the identifier of thefirst base station IdSB₁, as an identifier of a route allowing aconnection to the first base station SB₁. According to the BGP routingprotocol, such a route identifier is called a “Route Target”. Thus, inthis second embodiment of the invention, the route identifier used isthe identifier of the base station IdSB₁.

During a step F23, the unit of communications equipment PE1 receives,from the communications equipment PE₂, PE₃, PE₄, the respectiveidentifiers of the base station IdSB₂, of the base station IdSB₃, and ofthe base station IdSB₄, as route identifiers respectively allowingconnections to the base station SB₂, the base station SB₃, and the basestation SB₄.

During a step F24, the unit of communications equipment PE₁ implements astep for comparison of the identifiers of the base stations IdSB₂,IdSB₃, and IdSB₄, received during the step F23, with the identifier ofthe second base station IdSB₂ extracted from the message MSG, MSG1.

In the case where one of the broadcast identifiers of base stationsIdSB₂, IdSB₃ or Id SB₄ is identical to the identifier of the second basestation IdSB₂ extracted from the message MSG, MSG1, the unit ofcommunications equipment PE₁ stores, during a step F25, the identifierIdSB₂ of the route allowing a connection to the second base station SB₂.This step for storing the route for reaching the second base station SB₂completes the establishment of the link T between the first unit ofcommunications equipment PE₁ and the second unit of communicationsequipment PE₂.

In parallel, the base station SB₁ sends a message MSG to the mobilitymanagement equipment MME. The message MSG comprises the identifier ofthe base station SB₁ and the identifier of the base station SB₂ togetherwith information indicating that these two base stations SB₁, SB₂ areneighbors.

The mobility management equipment MME then transmits a message MSG′ tothe base station BS₂ during a step F26. This step allows the second basestation BS₂ to obtain the identifier IdSB₁ of the first base stationSB₁.

Upon receiving this message MSG′, the steps F1 to F25 previouslydescribed are implemented by the unit of communications equipment PE₂ inorder to establish the link T for the direction of communication—unit ofcommunications equipment PE₂ toward unit of communications equipmentPE₁—such that the link T is bidirectional.

Since the transport of the data via the link T is carried out accordingto the MPLS technique, each unit of communications equipment PE_(i) ofthe network R is identified by a label lbl_(i). This label lbl_(i),allows any given unit of communications equipment PE_(i) to establish aconnectivity according to the MPLS technique with another unit ofcommunications equipment.

Thus, once the link T is established between the unit of communicationsequipment PE₁ and PE₂, the latter exchange their respective labels lbl₁and lbl₂. The label lbl₁ is added by the second unit of communicationsequipment PE₂ in the header of the data intended to be sent toward thefirst unit of communications equipment PE₁ via the link T. Similarly,the label lbl₂ is added by the first unit of communications equipmentPE₁ in the header of the data intended to be sent to the second unit ofcommunications equipment PE₂ via the link T.

Since the link T thus established is an Ethernet connectivity, in orderto be able to transmit data between the unit of communications equipmentPE₁ and the unit of communications equipment PE₂, the base stations SB₁and SB₂ must inform one other of their physical addresses. A physicaladdress is for example a level 2 address such as a MAC (Medium AccessControl) address.

For this purpose, the base stations SB₁ and SB₂ exchange requestsconforming to the ARP (Address Resolution Protocol) protocol via thelink T during steps F27 and F28 allowing the MAC addresses of the basestations SB₁ and SB₂ to be learnt. Once the physical addresses of thebase stations SB₁ and SB₂ have been stored by the unit of communicationsequipment PE₁ and PE₂ in a VSI (Virtual Switching Instance) table, thetransmission of the data is possible.

During the transmission of data from the base station SB₁ to the basestation SB₂, the unit of communications equipment PE₁ adds the labellbl₁ in the header of the data intended to be sent to the base stationSB₂ together with the physical address of the base station SB₂ in orderthat the data sent are received on the port of the unit ofcommunications equipment PE₂ corresponding to the base station BS₂.

In a third embodiment of the invention shown in FIG. 7, the link T to beestablished between the unit of communications equipment PE₁ and theunit of communications equipment PE₂ is a pseudo-link MPLS such asdefined in the document RFC 3985 by the term “pseudo-wire”, allowing anEthernet connectivity supplied by the LDP L2VPN (Level 2 Virtual PrivateNetworks) service such as defined in the document RFC 4762.

In this third embodiment of the invention, the unit of communicationsequipment PE₁ extracts from a message MSG, MSG1, sent by the basestation SB₁, the identifier of the first base station IdSB₁, theidentifier of the second base station IdSB₂ during the step F1.

During a step G21, the unit of communications equipment PE₁ stores theidentifier IdSB₁ of the base station SB₁ and the identifier of the basestation IdSB₂ of the neighboring base station SB₂.

During a step G22, the unit of communications equipment PE₁ creates afirst point of attachment SAII of the pseudo-wire in the first unit ofcommunications equipment PE₁. Such a point of attachment has asidentifier the identifier of the base station IdSB₁.

During a step G23, the first unit of communications equipment PE₁determines an identifier of a second point of attachment TAII of thepseudo-wire in the second unit of communications equipment PE₂; such anidentifier of the point of attachment TAII is the identifier of the basestation IdSB₂ comprised in the message MSG, MSG1.

The establishment of the pseudo-wire is at the initiative of the firstunit of communications equipment PE₁ and relies, for example, on theexchange of requests for establishing a link conforming to the T-LDP(Label Distribution Protocol) protocol defined in the document of theIETF reference RFC 4447.

Thus, a first request for establishing the link SIG1 of the pseudo-wireis sent by the unit of communications equipment PE₁ to the unit ofcommunications equipment PE₂ during a step G24. This first request forestablishing the link SIG1 comprises the identifier SAII of the firstpoint of attachment of the pseudo-wire on the unit of communicationsequipment PE₁, and the identifier TAII of the second point of attachmentof the pseudo-wire on the unit of communications equipment PE₂. All ofthis information constitutes an FEC (Forwarding Equivalent Class)identifying the pseudo-wire T. The request for establishing the linkSIG1 also comprises a label lbl1.

The SAII and TAII of the points of attachment of the pseudo-wire T onthe units of communications equipment PE₁, PE₂ allow the request forestablishing the link SIG1 to be routed between the units ofcommunications equipment PE₁ and PE₂.

In parallel, the base station SB₁ sends a message MSG to the mobilitymanagement equipment MME. The message MSG comprises the identifier ofthe base station SB₁ and the identifier of the base station SB₂ togetherwith information indicating that these two base stations SB₁, SB₂ areneighbors.

The mobility management equipment MME then transmits a message MSG′ tothe base station SB₂ during a step G25. This step allows the second basestation SB₂ to obtain the identifier IdSB₁ of the first base stationSB₁.

Upon receiving this message MSG′, the steps F1 and G21 to G24 previouslydescribed are implemented by the unit of communications equipment PE₂ inorder to establish a pseudo-wire for the direction of communication—unitof communications equipment PE₂ toward unit of communications equipmentPE₁.

When data is transmitted via the pseudo-wire T, the label lbl₁ is addedby the second unit of communications equipment PE₂ in the header of thedata intended to be sent toward the first unit of communicationsequipment PE₁. Similarly, a label lbl₂ is added by the first unit ofcommunications equipment PE₁ in the header of the data intended to besent toward the second unit of communications equipment PE₂.

FIG. 8 shows a base station SB_(i) implementing the method ofcommunication which is a subject of the invention.

Such a base station SB_(i) comprises means of selection 10 of aneighboring base station from amongst a plurality of neighboring basestations according to the ANR technique.

The selection means 10 are connected to the input of first means ofgeneration 11 of a message MSG intended to be transmitted to themobility management equipment MME.

The selection means 10 are also connected to the input of second meansof generation 12 of a message MSG1 intended to be transmitted to theunit of communications equipment PE, to which the base station SB_(i) isconnected.

The first generation means 11 and the second generation means 12 areconnected to the input of means for transmission 13 of the messages MSGand MSG1 via the link L1.

FIG. 9A shows a unit of communications equipment PE_(i) implementing themethod for establishing a link which is a subject of the invention.

Such a unit of communications equipment PE_(i) comprises means 20 forreceiving or for intercepting a message MSG, MSG1 sent by the basestation SB, connected to the unit of communications equipment PE_(i).

The reception or interception means 20 are connected to the input ofmeans of extraction 21 of the identifier of the base station IdSB_(i)connected to the unit of communications equipment PE_(i), and theidentifier of the neighboring base station IdSB_(neighbor).

The extraction means 21 are connected to the input of means 22 forestablishing a link T between the unit of communications equipment PE,and the unit of communications equipment PE_(neighbor) to which isconnected the neighboring base station SB_(neighbor).

FIG. 9B shows a unit of communications equipment according to the firstand second embodiments of the invention.

Such a unit of communications equipment PE, comprises means 20 forreceiving or for intercepting a message MSG, MSG1 sent by the basestation SB_(i) connected to the unit of communications equipment PE_(i).

The reception or interception means 20 are connected to the input ofmeans of extraction 21 of the identifier of the base station IdSB_(i)connected to the unit of communications equipment PE_(i), and theidentifier of the neighboring base station IdSB_(neighbor).

The extraction means 21 are connected to the input of storage means 23for the identifier of the base station IdSB, and the identifier of theneighboring base station IdSB_(neighbor).

The storage means 23 are connected to the input ofbroadcasting/receiving means 24 capable of broadcasting, to othercommunications equipment, the identifier of the base station IdSB_(i) asan identifier of a route allowing a connection to the first base stationSB_(i).

The broadcasting/receiving means 24 are also capable of receiving, fromthe other communications equipment, the identifiers of the base stationsconnected to each of them, as route identifiers allowing a connection tothem.

The broadcasting/receiving means 24 are connected to the input of meansof comparison 25 of the identifiers of the base stations received by thebroadcasting/receiving means 24 with the identifier of the base stationIdSB_(neighbor) stored in the storage means 23.

In the case where one of the broadcast identifiers of base stations isidentical to the identifier of the base station IdSB_(neighbor)extracted, the unit of communications equipment PE, stores in thestorage means 23 the identifier IdSB_(neighbor) of the route allowing aconnection to the base station SB_(neighbor).

FIG. 9C shows a unit of communications equipment according to the thirdembodiment of the invention.

Such a unit of communications equipment PE_(i) comprises means 20 forreceiving or for intercepting a message MSG, MSG1 sent by the basestation SB_(i) connected to the unit of communications equipment PE_(i).

The reception or interception means 20 are connected to the input ofmeans of extraction 21 of the identifier of the base station IdSB_(i)connected to the unit of communications equipment PE_(i) and theidentifier of the neighboring base station IdSB_(neighbor).

The extraction means 21 are connected to the input of storage means 30for the identifier of the base station IdSB_(i) and the identifier ofthe neighboring base station IdSB_(neighbor).

The storage means 30 are connected to the input of means 31 for creationof a first point of attachment SAII of the pseudo-wire in the unit ofcommunications equipment PE_(i). Such a point of attachment has asidentifier the identifier of the base station IdSB_(i).

The storage means 30 are also connected to the input of means 32 fordetermining an identifier of a point of attachment TAII of thepseudo-wire in the unit of communications equipment PE_(neighbor). Suchan identifier of the point of attachment TAII is the identifier of thebase station IdSB_(neighbor) comprised in the message MSG, MSG1.

The creation means 31 and the determination means 32 are connected tothe input of means of transmission 34 of a request for establishing apseudo-wire T.

1. A method for establishing a link in an Open Systems Interconnection(OSI) layer 2 or 3 via which at least one data stream is intended to betransmitted, a first unit of communications equipment and a second unitof communications equipment respectively forming a first and a secondend of the link, a first base station being connected to the first unitof communications equipment, and a second base station being connectedto the second unit of communications equipment, wherein the first basestation has selected the second base station from amongst a plurality ofbase stations in anticipation of a handover procedure, the methodimplemented by the first unit of communications equipment andcomprising: extract an identifier of the first base station and anidentifier of the second base station comprised in a message transmittedby the first base station, establishing the link between the first unitof communications equipment and the second unit of communicationsequipment based on the identifier of the first base station and on theidentifier of the second base station extracted.
 2. The method forestablishing a link as claimed in claim 1, wherein establishing the linkcomprises: broadcasting to a plurality of communications equipment theidentifier of the first base station as an identifier of a routeallowing a connection to the first base station, comparing an identifierof another base station, broadcast to a plurality of communicationsequipment including the first unit of communications equipment byanother unit of communications equipment as an identifier of a routeallowing a connection to the other base station, with the identifier ofthe second base station extracted, and wherein when the identifier ofthe base station broadcast is identical to the identifier of the secondbase station extracted, storing the identifier of the route allowing aconnection to the second base station.
 3. The method for establishing alink as claimed in claim 1, wherein establishing the link comprises:creating a first point of attachment in the first unit of communicationsequipment intended to form the first end of the link, determining anidentifier of a second point of attachment in the second unit ofcommunications equipment intended to form the second end of the link,and sending a request for establishing the link to the second unit ofcommunications equipment, the request for establishing the linkcomprising the identifier of the first point of attachment and theidentifier of the second point of attachment.
 4. A method ofcommunication between a base station and a unit of communicationsequipment to which the base station is connected, the base stationselected from amongst a plurality of base stations, in anticipation of ahandover procedure, a second base station connected to a second unit ofcommunications equipment, a link in the Open Systems Interconnection(OSI) layer 2 or 3 via which at least one data stream is intended to betransmitted, the link being intended to be established between the firstand the second unit of communications equipment, wherein the methodcomprises sending a message to the first unit of communicationsequipment, the message comprising an identifier of the first basestation and an identifier of the second base station.
 5. A unit ofcommunications equipment forming a first end of a link in the OpenSystems Interconnection (OSI) layer 2 or 3 via which at least one datastream is intended to be transmitted, a second unit of communicationsequipment forming a second end of the link, a first base station beingconnected to the unit of communications equipment, and a second basestation being connected to the second unit of communications equipment,wherein the first base station has selected the second base station fromamongst a plurality of base stations in anticipation of a handoverprocedure, wherein the unit of communications equipment is configuredto: extract an identifier of the first base station and an identifier ofthe second base station comprised in a message sent by the first basestation, and establish the link between the unit of communicationsequipment and the second unit of communications equipment based on theidentifier of the first base station and on the identifier of the secondbase station extracted.
 6. A base station, connected to a first unit ofcommunications equipment and selected from amongst a plurality of basestations, in anticipation of a handover procedure, a second base stationconnected to a second unit of communications equipment, a link in theOpen Systems Interconnection (OSI) layer 2 or 3 via which at least onedata stream is intended to be transmitted, the link being intended to beestablished between the first and the second unit of communicationsequipment, wherein the base station is configured to send a message tothe first unit of communications equipment, the message comprising anidentifier of the first base station and an identifier of the secondbase station.
 7. A computer program product comprisingcomputer-executable instructions that, when executed by a processor,implement the method for establishing a link as claimed in claim 1 whenthe program is executed by a processor.
 8. A non-transitorycomputer-readable medium configured to be read by a unit of switchingequipment on which the computer program product as claimed in claim 7 isrecorded.
 9. A computer program product comprising computer-executableinstructions that, when executed by a processor, implement the method ofcommunication as claimed in claim
 4. 10. A non-transitory recordingmedium readable by a unit of switching equipment on which the computerprogram product as claimed in claim 9 is recorded.